To understand why decompilers exist for GameMaker and not as easily for other engines like Unreal or Unity, one must look at the architecture of the engine itself.
You can then open it in Game Maker Studio (if version matches) and edit. Game maker exe decompiler
The feasibility of decompilation depends heavily on the version of the engine and the specific export method used. To understand why decompilers exist for GameMaker and
✅ (with permission or clear rights):
is particularly notable: it was built for modding Undertale (made in GMS 1) but works on many GMS 1.x/2.x games, allowing decompilation of scripts, editing textures, and repacking. allowing decompilation of scripts